1. Field of the Invention
The present invention pertains to an improved high pressure pump for continuously pumping fluids at high pressure. More particularly, the invention relates to the application of a novel piston-cylinder combination which reduces galling and component wear while increasing the overall efficiency and service life of pumps. The reduction in galling is achieved by reducing the diameter of the piston or increasing the inside diameter of the cylinder or both to provide about a 0.1 percent to 2.5 percent increase in clearance at the pressure end of the piston-cylinder combination than is provided by a centering area. The centering area is axially displaced from the pressure end of the piston-cylinder combination and may similarly be formed by modifying the diameter of the piston or cylinder or both to provide a centering area having a 0.1 percent to 2.5 percent closer clearance than the pressure end of the piston-cylinder combination.
The advantages of the present invention are further augmented by providing a release area intermediate the pressure end and the centering area of the piston-cylinder combination. The release area may be formed in the piston-cylinder combination by decreasing the diameter of the piston or increasing the inside diameter of the cylinder or both to provide a chamber. The chamber provided in the preferred embodiment is of an axial length sufficient to accommodate the length of the stroke of the piston and is arranged to accommodate the length of travel of any ridge resulting from a change in piston diameter between the pressure end of the piston and the centering area of the piston-cylinder combination.
The novel piston-cylinder combination is designed to allow the piston to reciprocate in the release area which is slightly longer than the stroke of the piston and allows the area of demarcation on the piston to reciprocate in the release area without touching the cylinder wall and allows the pressure end of the piston to operate without touching the inside diameter of the sleeve to a degree that would result in seizure or galling. The release area in conjunction with the area of demarcation of the novel piston operates in the pressure end of the piston-cylinder combination in such a manner as to allow the pressure end of the piston to essentially operate free from lubricating contamination and galling while providing a release area which allows collected lubricating fluids to drain from the cylinder and minimize the possibility of lubricating fluid contamination in the event of a seal failure.
2. Description of the Prior Art
The prior art includes a variety of mechanical devices for centering pistons in pumps and increasing the sealing properties of the piston and cylinder arrangement. It is recognized that the effectiveness and efficiency of the pumps are increased by properly centering the piston and providing a more effective seal for the piston. Exemplary of one such approach in the prior art to increase the efficiency of the pumps is U.S. Pat. No. 3,916,771 which utilizes a deformable sealing sleeve employed in conjunction with an ordinary piston that is designed to limit the radial and angular displacement of the piston. A deformable sleeve is disposed in a axial channel provided in the housing that surrounds the piston.
Unlike the present invention, the axial cavity provided in U.S. Pat. No. 3,916,771 does not function as a release area and is not by itself for the purpose of reducing galling. In contrast to the cavity provided in the housing of the prior art for accommodating a sealing sleeve or liner, the present invention employs a release area to provide the dual function of reducing galling by cooperating with the modified piston-cylinder combination and which further cooperates with the piston-cylinder combination to provide a fluid discharge area in the event of seal failure to prevent the contamination of the lubricating fluid with a non-lubricating fluid. Furthermore, the prior art unlike the present invention does not utilize a specially designed piston for cooperation with a cylinder and a release area in the cylinder to accomplish the results of the present invention. More particularly, the prior art has generally employed pistons of the same diameter whereas the present invention utilizes modifications of the piston-cylinder combination to provide for the centering of the piston and a reduction of the galling potential in pumps.
In U.S. Pat. No. 3,902,404 a deformable sleeve is provided for surrounding a piston of a uniform diameter to improve the sealability of the pump in high and low pressure ranges. A series of peripheral grooves 19a are provided in a deformable sleeve to assist in the centering of the piston which as described in the prior art patent is particularly useful at low pressure operations. Unlike the prior art, the present invention employs a piston of a slightly reduced circumferential diameter to reduce component wear. Centering of the piston in prior art Patent 3,902,404 is provided for in a manner that is similar to U.S. Pat. No. 3,916,771. The present invention unlike these prior art patents provides a novel arrangement of elements and the utilization of the piston-cylinder combination in an area of reduced pressure for centering the piston and thereafter utilizing a greater clearance at the pressure end of the piston-cylinder combination for reducing galling and component wear of novel pumps constructed in accordance with the invention.
In U.S. Pat. No. 3,811,798, the pump disclosed utilizes a piston of reduced diameter having a means for sealing the pumped fluid from the lubricating fluid. The manner in which this prior art patent accomplishes its objectives is the utilization of a slidable O-ring for opening and closing a lubricant return passageway disposed between the cylinder bore and a passage which is opened and closed by the reciprocating action of the piston. U.S. Pat. No. 3,811,798 employs a piston having two portions of different diameter but unlike the present invention does not utilize a piston-cylinder combination to provide the advantages of the present invention. In U.S. Pat. No. 3,811,798 the cylinder is divided into two chambers by an annular member 93. The pressure end of the piston operates predominantly in the pressure portion of the piston-cylinder combination while the wider diameter portion 77 reciprocates in portion 64 of the cylinder. The size of bore 64 in relation to bore 80 is not specified, however the difference in size of the piston is specified as being about 0.010 inches smaller. Even assuming a cylinder of a uniform bore, which appears contrary to the teaching on column 4 lines 60-63, the present invention is distinguishable from the prior art in the arrangement and provision of additional components to provide the advantages of the invention. Furthermore the invention described in U.S. Pat. No. 3,811,798 is not for the relationship in the cylindrical bore but instead for the sliding O-ring valve 68.
The present invention in contrast employs a piston-cylinder combination of two different diameters which cooperate in a pressure area and centering area in combination with a release area. Unlike the prior art, the present invention provides a release area to accommodate the reciprocation of the area of demarcation between the larger and smaller diameter portions of the piston. The utilization of a sleeve of a substantially uniform diameter except for the release area operates to achieve the advantages of the present invention over the prior art. The release area further serves as an area to prevent the contamination of the pumped fluid from the lubricating fluid in the event of seal failure while providing a release area of an axial length sufficient to allow the larger portion of the piston to operate in a release area to reduce piston to cylinder wall contact and increase component life. Similarly, the forward end of the piston being of a reduced diameter has already been centered by the action of the centering area of the piston-cylinder combination located away from the pressure area of the piston-cylinder combination which allows the pump to operate more effectively.
The prior art pump and piston-cylinder combinations generally focus on the problem of increasing the efficiency of the seal or the problem of centering the piston as a means for increasing the efficiency of the components and decreasing the potential for galling. The present invention in contrast divides the piston into a pressure end and a driving or centering end and modifies the piston-cylinder combination by reducing the diameter of the piston or increasing the inside diameter of the cylinder or both at or near the pressure end of the piston-cylinder combination and providing a release area between the pressure end and centering portion of the piston-cylinder combination which the axial length of in combination with the release area is designed to accommodate the stroke or length of travel of the ridge formed between the larger diameter and the smaller diameter portions of the piston. This combination of elements operates to simultaneously increase the efficiency of the seal system and additionally provides a valuable back up in the event of seal failure while providing the advantages incumbent in a pump which exhibits a decreased tendency to seize or to gall.
In one embodiment of the invention a small diameter pressure end of a piston is utilized to provide a larger clearance in the pressure end of the piston-cylinder combination in conjunction with the piston centering advantages achieved by utilizing a larger diameter portion of the piston in the rearward portion of the sleeve to provide a smaller clearance in the piston-cylinder combination at the centering area to increase seal efficiency by reducing the incidence of cylinder wall scarring by the piston. Furthermore, the disposition of the stepped portion of the piston in the release area further increases component life by assuring that frictional vibrations and losses are kept to a minimum while providing an important back-up system in the event of seal failure.
The release area further serves as a lubricant or oil drain from the cylinder area and prevents the contamination of the lubricating fluid and pumped fluids. The configuration of the novel piston in conjunction with the release area even more importantly reduces the number and wear on seals and the consequent cost in manufacture and maintenance of the pump while removing the major cause of galling and pump seizure. These advantages are achieved utilizing a novel design which furthermore reduces the cost of manufacturing and assemblage of the novel pump while increasing the service life of the piston-cylinder components.